The porous spherical polyamide particles are studied for the use as components for cosmetics such as cleansing mask or for packing material for chromatographic apparatus. Further, the porous spherical polyamide particles are studied for the use as catalyst carriers or adsorbents in food industry and medical fields. Furthermore, the porous spherical polyamide particles are studied for the use as carriers for coloring materials to provide a toner for electrographic duplicating machines or to provide material for display devices.
It is known that the porous spherical polyamide particles can be produced by a solvent-induced phase separation process. The solvent-induced phase separation process comprises mixing a polyamide solution comprising polyamide dissolved in a solvent and a solvent that is a poor solvent (or a non-solvent) for the polyamide but compatible with the solvent, to cause phase separation, whereby precipitating porous spherical polyamide particles. It is said that the solvent-induced phase separation process is advantageous because uniform porous spherical polyamide particles can be easily produced by appropriately selecting the solvent for polyamide and the poor solvent.
Japanese patent provisional publication 3-26729 discloses a process for producing porous polymer microparticles which comprises uniformly dispersing a polymer solution which is prepared by dissolving crystalline polymer in a solvent (first solvent) in a poor solvent (second solvent) having a higher hydrogen-bonding factor than that of the first solvent. The working examples of the Japanese publication describe a process for producing porous spherical polyamide 66 (nylon 66) particles using dimethylformamide (as first solvent) and ethylene glycol monomethyl ether (as poor solvent).
Japanese patent provisional publication 2002-80629 discloses a process for producing porous spherical polyamide particles which comprises the steps of mixing a polyamide solution with water and a poor solvent for polyamide to give a temporarily uniform solution and precipitating the polymer. The working examples of the Japanese publication describe a process for producing porous spherical particles of polyamide 6 (nylon 6) or polyamide 66 using m-cresol or formic acid as the solvent and methanol as the poor solvent.
Polyamide 11 (nylon 11) and polyamide 12 (nylon 12) are advantageous over polyamide 6 and polyamide 11 from the view point of low moisture absorption.
The present inventors found, however, that the known solvent-induced phase separation process applied to polyamide 11 or polyamide 12 insufficiently precipitate the porous particles and further the precipitated porous primary particles are apt to aggregate.